Strain Isolation and Study on Process Parameters for Xylose-to-Xylitol Bioconversion

Abstract

ABSTRACTA xylitol producing yeast was isolated from soil and identified as Candida tropicalis W103 by 18S r DNA gene sequence analysis and physiological characteristics. The optimal fermentation conditions for Candida tropicalis W103 were: 35°C, pH 4.5 and 120 g l−1 initial xylose concentration. However, the maximum yield and productivity of xylitol were obtained at KLa 16.5 h−1 and 18.3 h−1, respectively. A two-stage aeration strategy (0–24 h, KLa 18.3 h−1; after 24 h, shift KLa to 16.5 min−1) was applied in the fermentation to get higher xylitol yield and productivity. After 60 h in batch fermentations, both the xylitol concentration and xylose consumption reached the maximum, obtaining 87.1 g l−1 of xylitol with 1.45 g l−1 h−1 productivity and 0.72 g g−1 xylose yield. Fed-batch fermentation with 120 g l−1 initial xylose and regulating xylose concentration to 40–55 g l−1 during 24–96 h was performed to reach a higher productivity of 1.82 g l−1 h−1, and xylitol concentration of 218.7 g l−1.